Many devices exist that inject a signal onto a length of wire or pair of wires for the purpose of physically locating other parts of the length thereof. These devices are commonly called `tone generators`, even though these devices themselves only produce an electrical signal and a receiver functions to produce the actual audible tone. U.S. Pat. No. 5,457,441, for example, discloses a receiver of the inductive pick-up type which produces a tone when it picks up a signal. A receiver can be incorporated as part of a standard telephone test set or other common test equipment. Such a process is used when the location of one end of a cable or wire is known and the location of the other end is not known or is closely bundled with other cables or wires and can not be specifically identified.
To illustrate, consider the simple situation of a pair of wires isolated at one end and grouped with a few other pairs at the other end. The `tone generator` is connected to the isolated end of the pair of wires and the receiver is placed near the group of wires at the other end. The receiver is positioned closely adjacent to each wire sequentially, and when the tone output of the receiver is loudest, one might reasonably conclude that the receiver is closest to the wire in question.
While this process often works well, it fails when the wires are in sufficient proximity for the injected signal to couple across to one or more of them. In that case, the tone output of the receiver is often equally loud when placed near many of the wires and identification is not possible. In the not so simple case where the known end of the wires is already bundled in a large quantity of wires, and this bundle along with other bundles are routed in close proximity for a long length, the process almost always fails, allowing a tone to be produced from the signal on many of the wires. While this failed process has often reduced the count of possible solutions, it sometimes does not.
The next process usually followed by the person interested in finding the wires is to individually test the wires by placing a short on the known end and measuring for that short on the possible unknown ends. This process requires that the person make several trips from one end of the wiring to the other. These trips can involve flights of stairs, or even be between buildings. This is clearly an inefficient process.
There exist expensive and complex devices that allow for the remote changing of the injected signal but require special instrumentation at the remote end. See, for example, the arrangement disclosed in U.S. Pat. No. 4,862,491. There are also remotely controllable signal generators that are used for the testing of telephone lines that require specific instrumentation at the remote end to affect that change in the signal generator. See, for example, U.S. Pat. No. 5,307,398. These existing methods and devices require specific and expensive pieces of test equipment that may be justified for use by test technicians, but are not generally in the possession of ordinary households. Yet, there exists in ordinary households the need to identify wires in the course of owner-performed home improvements or repair.
This invention provides a solution to the problem of positive identification of wires without regard to the characteristics of the wire type or the intended use of the wires, and with no additional instrumentation being required at the remote end. When appropriately implemented in a signal generator or detector employed in other types of equipment, such as multimeters or time domain reflectometers (TDR's), there is minimal or no additional cost to that signal generator or detector. This allows for the low cost inclusion of this wire location/identification capability in an existing piece of test equipment suitable for home or professional use.